1. Field of the Invention
The present invention relates to a method for monitoring unusual signs such as partial heatings and electric discharges in a gas-charged apparatus such as a gas-insulated transformer, gas-insulated switchgear, gas circuit breaters and turbine and the like, and a gas-charged apparatus including an unusual sign monitor for catching the unusual signs.
2. Description for the Background Art
In a conventional oil-immersed electric apparatus such as a transformer, a main body is contained in a tank filled with an insulating oil for insulating and cooling the main body. When anything unusual such as a trouble with an unusual heating or a partial electric discharge by a corona arc happens in the tank, the insulating oil is ignited to cause an explosion, and, in the worst case, the insulating oil is scattered in all directions to bring about a secondary accident such as a fire of surrounding buildings and the like. Nowadays, as the electric power demand largely increases, it becomes difficult to ensure the installation place for such electric apparatuses, and thus the electric apparatuses such as the transformer are often installed in the surroundings of the streets or the underground of the buildings. Accordingly, the electric apparatus having a higher safety, which is capable of preventing a fire and environmental disruption, has been demanded.
In order to satisfy these demands, a gas-insulated electric apparatus such as a transformer, which is compact, light in weight and much reliable with the prevention of disasters as compared with the oil-immersed electric apparatus, has been employed. In such a gas-insulated electric apparatus, a main body is equipped within a container, and an insulating gas as an insulating and cooling medium for the main body is enclosed in the container instead of the conventional insulating oil. This insulating gas requires (1) a high dielectric strength, (2) a thermal stability and inertness, (3) a nonflammability, (4) a harmlessness to a human being, (5) a good thermal conductivity and so forth. For instance, a gas SF.sub.6 satisfying these properties is used in the electric apparatus such as the transformer. Hence , in the gas-insulated electric apparaus, even when the temperature in the container increases to abnormally high due to an occurrance of a trouble therein, there is no feat to cause a fire, and no bad influence is given to the surroundings. Thus, the gas-insulated apparatus may be suitably installed in the streets and the underground of the buildings.
In the electric apparatus such as the transformer, the stop of the operation due to the accident or trouble should be completely avoided from the standpoint of the stable power supply. It is apparent from the importance of the electric power energy that a stoppage of power supply due to an accident affects a number of bad social and economical influences to a various portions concerned. In case of a transformer, an eddy current is generated in the structural members of the body and container by a leakage flux to cause many abnormalities such as unusual partial heatings and a generation of heat due to incomplete contact of the conductive members or due to an insulation deterioration caused by a partial electric discharge. These abnormal states bring about a big accident to cause the power stoppage. Therefore, in the electric apparatus, it is necessary to provide an abnormality monitoring technique which always monitors occurrence of abnormalities in order to detect signs of troubles in the slight stages, and takes necessary measure to prevent an accident from occurring. Consequently, the reliability of the electric apparatus is further raised and the stable power supply can be achieved.
In the conventional oil-immersed electric apparatus such as the transformer, the abnormality monitoring is conducted as follows. That is, when a slight local heating as a premonitory stage following an accident is generated, the insulating oil is heated, and, when the temperature of the heated insulating oil is raised to 150.degree. to 200.degree. C., the insulating oil is decomposed to generate a gas. Then, the generated gas is always or periodically detected, thereby monitoring the abnormality of the apparatus.
In the conventional gas-insulated electric apparatus, the insulating gas enclosed in the tank is always or periodically analyzed to perform the abnormality monitoring. However, as described above, the insulating gas such as SF.sub.6 gas is thermally stable and inert, which means the insulating gas is not decomposed by the slight local heating. This is disadvantageous in the abnormality monitoring. That is, it is quite difficult to detect the premonitory stage of the slight trouble or accident by analyzing the insulating gas.
Further, when the abnormality monitoring is carried out, it is necessary to able to monitor the abnormalities such as local heating not only in predictable portions but also unexpected portions. The electric apparatus such the gas-insulated transformer is designed with sufficient thermal strength and insulating strength, but an occurrence of troubles in the unexpected portions can not be ignored. The detection and prevention of such unexpected troubles largely improve the reliability of the apparatus.